package com.testDemo.thread.concurrent;

import org.junit.jupiter.api.Test;

import java.util.concurrent.CountDownLatch;

/**CountDownLatch类位于java.util.concurrent包下，利用它可以实现类似计数器的功能。比如有一个任务A，它要等待其他4个任务执行完毕之后才能执行，此时就可以利用CountDownLatch来实现这种功能了
 * 　然后下面这3个方法是CountDownLatch类中最重要的方法：
 * public void await() throws InterruptedException { };   //调用await()方法的线程会被挂起，它会等待直到count值为0才继续执行
 * public boolean await(long timeout, TimeUnit unit) throws InterruptedException { };  //和await()类似，只不过等待一定的时间后count值还没变为0的话就会继续执行
 * public void countDown() { };  //将count值减1
 *
 * @Auther: zouren
 * @Date: 2019/3/15 10:56
 * @Description:
 */
public class CountDownLatchTest {
    @Test
    public void countDownLatch() {
        //参数count为计数值
        final CountDownLatch latch = new CountDownLatch(2);

        new Thread() {
            public void run() {
                try {
                    System.out.println("子线程" + Thread.currentThread().getName() + "正在执行");
                    Thread.sleep(3000);
                    System.out.println("子线程" + Thread.currentThread().getName() + "执行完毕");
                    latch.countDown();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }

            ;
        }.start();

        new Thread() {
            public void run() {
                try {
                    System.out.println("子线程" + Thread.currentThread().getName() + "正在执行");
                    Thread.sleep(3000);
                    System.out.println("子线程" + Thread.currentThread().getName() + "执行完毕");
                    latch.countDown();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }

            ;
        }.start();

        try {
            System.out.println("等待2个子线程执行完毕...");
            latch.await();//调用await()方法的线程会被挂起，它会等待直到count值为0才继续执行
            System.out.println("2个子线程已经执行完毕");
            System.out.println("继续执行主线程");
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
}

